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Unformatted text preview: Physics 112 Test 3
Physics for Scientists and Engineers Dr. Clark
17 October 2005 Do all problems. Circle the correct answer for multiple choice questions (box in a second
choice for potential partial credit). Show all work and explain your reasoning to receive
full credit. If you do not understand a question or find it ambiguous, ask the monitor
about it. A. Multiple Choice Problems: (8 points each)
1. You want to reﬂect a laser beam without changing its polarization. Which of the
following would work? a. Reﬂect the beam from a thin film 1%: wavelength thick.
® Reﬂect the beam using total internal reﬂection. /
c. Make sure the beam is incident from air to a reﬂector with lower refractive index than
glass.
d. Reﬂect the beam twice so the phase changes cancel out. 6. Make sure the beam is incident from air at Brewster's angle to the reﬂecting surface
normal. 2. The double slit interference experiment is performed in a spaceship at rest and then
moving at 0.5 c with respect to Dr. Clark’s home planet. Which is true for an observer in
the spaceship when it is moving. relative to when the ship is stationary? a. The intensity of the maxima would be further apart.
Q3) The interference patterns would be identical.
c. You could no longer use phasors to find the minima and maxima.
d. The interference maxima would be closer together because of length contraction.
e. The observer would see a rainbow effect like on Star Trek. 3. White light shines from air onto a thin layer of mineral oil on top of a piece of plastic,
yielding some colorful reﬂections. As the mineral oil layer spreads out it gets thinner.
Eventually, there is no reﬂected light. What can be concluded from these observations? (3. Mineral oil has a higher refractive index than the plastic. b. The film is so thin that its refractive index is essentially the same as air. 0. Mineral oil has a lower refractive index than the plastic. d. The mineral oil film has evaporated. e. You really cannot conclude anything unless you know the oil ﬁlm thickness. «.AJmé: [A It]! r». u »‘ '1 “his i "%‘i_'4 ‘i 3 ' r rm“ hue). (t. r r  _ “I.
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_ ___. r _ _ ___ _ (/1 inc 0 \ <3 IE. i (24 :lulL an; 4. Monochromatic light is incident on an adjustable single slit producing many bright
bands on a screen. Which is most likely true? a. The bands get dimmer as the slit width is increased. U 0 03) The bands get closer together as the slit width is increased. vibe“ c. As the width of the slit is increased from zero, the bands ﬁrst get farter apart and then
closer together as the distance of greatest resolution is reached. N0 d. Bands will only be observed when the slit width is smaller than the wavelength of the
light. N0 5. To get the primary maxima closer together in a multiple slit experiment you could _ as Q Increase the spacing between slits.\/ fl .. b. Increase the wavelength of the light.“0 L _
c. Increase the distance to the screen." 0 /7\ .\ gm u, maxi/wt; «weKW“
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f. Increase the 1ncom1ng 1ntensrty. W \—— “CAL "A ' at x b‘ﬂ ‘ I B. Short Calculations: (8 points each) 6. Consider a single slit diffraction experiment with light of wavelength 600 nm, slit
width 0200 mm, and a screen 1.00 m away from the slit. How many bright fringes are
there between the points that are 3.00 and 10.00 cm above it? )1 {ooafnrn
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by d : 0.20 mm. What is the separation between adjacent minima between the 5th and
6th principal maxima on a screen 4.00 m away? 4.. d“ i\\¢ l .
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9. Astronomers announce the discovery of an asteroid, 7.00 X 1015 km away, traveling toward the Earth with a speed 0.850c. How far is it from the Earth, as measured by one
of Dr. Holland's cows in the asteroid frame? _ L Lt L {Zan‘ 10. Consider a single slit diffraction experiment with light of wavelength 500 nm, slit
width 0.100 mm, and a screen 3.00 m away from the slit. What is the intensity at an
angle of 0.00700 rad below the center of the central maximum if the intensity of the central maxima is l Watt/m2? F 9;} p12 {5 _ 27,2, a <38
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image forms on the screen a distance L, away. Assume the light is in phase at each slit,
but that the amplitude is E; at the outer two slits and E; for the center slit. Show that the
amplitude of the light as it hits the screen is E = (E; +2E0 cos g5) cos (lacmt), Where ¢ is the phase angle relative to the center slit and the other variable have their
normal meaning. Assume the ﬁeld from the center slit is represented as E 1 cos (kx wt). Sketch both the amplitude and the intensity as a function of phase angle, at for E 1 : 2 E0
and 0 5 ¢ 5 27r. Do the same for E; : E0. .H _ t_
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at 600.000000 nm from a spectral line at 600.060000 nm in ﬁrst order? What is the slit
spacing if a 25 mm grating is employed? What is the angular separation between these
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This note was uploaded on 03/12/2010 for the course PHY 112 taught by Professor Staff during the Spring '08 term at Illinois State.
 Spring '08
 Staff
 Physics

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